1. Field of the Invention
The present invention relates to a lamp unit which comprises a light source unit for use in optical devices and the like, and a projection display apparatus which comprises the lamp unit, and more particularly, to a lamp unit which restrains noise generated by a cooling fan, and a projection display apparatus which is reduced in size and noise.
2. Description of the Related Art
Electric home appliances and the like are required be silent, so that a variety of technologies have been developed for reducing the generation of noise. This tendency goes beyond electric home appliances and is spreading to general electronic devices. In particular, for devices associated with personal computers, quiet operation is required not only for a magnetic disk drive, a CPU cooling unit, and a power supply cooling unit, which are components of a personal computer, but also for a projection display apparatus and the like which are connected to the personal computer for use therewith.
A projection display apparatus has a light source unit which acts as a particularly large heat source, and must therefore be cooled down in order to ensure its performance and reliability. Cooling methods for use with the projection display apparatus can be roughly classified into air cooling and liquid cooling (including water cooling). For air-cooling electronic devices, air cooling methods for use therewith can be sub-divided into natural air cooling and forced air cooling. The forced air cooling involves the use of a variety of fans for forcedly exposing objects that are being cooled to air, or for exhausting air heated within the device. Since this cooling fan generates noise, an attempt to enhance cooling capabilities of an electronic device can result in a problem of noisiness caused by noise generated from the cooling fan. This tendency is prominent in electronic devices equipped with large heat sources, and becomes more prominent as the device itself become smaller. The problem for a projection display device is the issue of how to reconcile a reduction in size with a reduction in noise which increases because of cooling mechanisms that are included in such devices in order to improve performance.
Generally, a plurality of axial flow fans have been used for cooling a projection display apparatus. For example, a projection display apparatus using a liquid crystal display device requires a fan for taking in cooling air from the outside to the liquid crystal display device through an air filter, and a fan for exhausting heated air within the apparatus. Also, in some cases, another auxiliary fan has been used. Due to such a structure, the exhaust fan is generally placed near the component that is heated to high temperatures.
JP-A-11-354963 discloses a projection display apparatus which does not use axial flow fans but comprises a multiblade fan and a cooling duct, and is cooled by a cooling method which excels in maintenanceability and usability, where cooling air from an area that is being cooled flows through the cooling duct in a direction in which the cooling air is sucked into the multiblade fan and exhausted out of the apparatus from an exhaust port provided through a front panel of the apparatus. Thus, the axial flow fan and multiblade fan are used for cooling fans. Generally, the multiblade fan as compared with the axial flow fan is often used for cooling a device which has large internal resistance because of its ability to provide a high static pressure.
For addressing a reduction in noise in the projection display apparatus, JP-A-10-197953 discloses a technique of restraining noise with the provision of a lattice member which has a plurality of rectangular or circular openings on the upstream side of an air path remote from an exhaust fan. JP-A-2000-035614 in turn discloses a technique for restraining noise by a reticular rectifier attached to an end face which is located away from the leeward side which air passes through a heat sink. JP-A-2001-142147 further discloses a technique for restraining noise by attaching a silencer box formed with an air pass chamber through which air is exhausted.
JP-A-2005-62452 discloses a technique for eliminating fine adjustments to a lamp optical axis with the help of the structure of a reflector holding member. A lamp unit is provided with lamp cooling holes and an intake port. Cooling air introduced through the lamp cooling holes arranged in a radial configuration locally cools down the area that surrounds the cathode of a light source lamp. The cooling air introduced through the intake port cools down the periphery of a reflector, and is exhausted from an exhaust port of the reflector cover.
However, the related art techniques described above have the following problems.
The first problem is the increased noise value in a small projection display apparatus resulting from the need for rotating a plurality of mountable small axial flow fans in order to produce the amount of exhaust air required to cool the projection display apparatus which is equipped with a large heat source. While this problem is in part caused by lack of an absolute amount of air provided by a small fan at an ordinary rotational speed, the problem is also largely affected by use of both the project apparatus and the exhaust fan for cooling the lamp which generates a large amount of heat. Also, the rotation of the fan at high rotational speeds is likely to generate grating noise. Therefore, even when the noise level is reduced, the noise is heard as annoying because of its grating nature. Also, it is difficult to employ a silencer attached to the apparatus for restraining such noise, due to limitations in the size of the apparatus.
A second problem is difficulties in equipping a small projection display apparatus with a fan which has sufficient capabilities of cooling a lamp. This problem stems from the fact that although the only way to provide required static pressure with a small fan is to sacrifice a certain amount of air, the conventional lamp cooling method involves increasing static pressure for ensuring a flow velocity required for cooling the lamp, whereas the amount of air cannot be reduced for cooling down generated heat.
A third problem lies in that even in JP-A-2005-62452 which discloses a technique for eliminating fine adjustments to a lamp optical axis, all cooling air does not pass through the cooling holes or intake port, so that portions of the cooling air which do not pass through the cooling holes or intake port become substantially useless, thus failing to effectively make use of a large amount of air. This causes a problem of generating lauder noise, as in the case of the foregoing first problem.